If I were competent enough to somehow be on death row for my crimes, I'd probably be competent enough to somehow use my last meal as a weapon. I'm trying to figure that out, however.
Well you could order a porterhouse, cayenne pepper, a peanut butter sandwich and some sort of shellfish. Take the steak bone and fashion it into a shank, find a way to dry out the pepper
(since last meals are served a day beforehand I think) to grind down into a powder to blow in the person's face, lather the bone-shank with peanut butter and fish stuff
(just in case the person is allergic), and bingo, last meal assault kit!